The invention relates generally to wireless communications and more specifically to techniques for determining the location of a mobile receiver in a wireless communications system.
Cellular telephones, portable computers, and other portable communications units benefit from the ability to independently determine their location. Most techniques for locating wireless receivers are directed at outdoor environments, such as for cellular telephones and vehicle-mounted receivers. However, some research has been directed toward creating separate indoor sensor networks for indoor positioning. A primary initiative for these efforts is the fact that low earth orbit (LEO) based Global Positioning System (GPS) has poor indoor coverage. Similar efforts have studied local wireless area network infrastructures that can be used for indoor location estimation by leveraging the information obtained via received wireless beacon signals.
In the case of cellular telephones, the ability to determine at least a rough location is a necessary one, so that handoffs can be made as the handheld unit moves from cell to cell. For similar reasons, portable computers connected to a network have an increasing need for the ability to estimate their locations in real time. For example, it would be helpful for a portable computer connected to a building's wireless network to be able to determine accurately its own location. Thus, it could determine which wireless access point is closest, thereby allowing for more robust connectivity to the wireless network. In other applications, portable computers, personal digital assistants, cordless telephones, cellular telephones, and other portable network devices would benefit from the ability to provide accurate location information to a user and to applications that can use the real-time information.